Re: Q



mebratziujane@xxxxxxxxx wrote:


The Williamson set up for class A UL could give 20 watts of class A1 po
into 4ka-a with the right OPT and you immediately had just as good an
amp compared to Quad-II. Home constructors who could think for
themselves could cope with winding filter chokes and odd sized R&C by
paralleling C or R to get a wanted value outside standard values.

There were plenty of OPT available in 1960 at least equal to the entry
level Hammonds of today, and many companies offered OPT with wider BW
than today's standard lowest common denominator, and these meant UL amps
with 15dB of GNFB were more easily made stable by the home amateur.

The Quad-II OPT is a bit too small. It saturates at too high an F at
full rated power, and HF performance is only barely adequate.
The winding resistance losses are way too high. Basically, their OPT are
toys compared to what should be there if best practices had been
followed as laid down in RDH4. The use of CFB windings *IS GOOD* though,
but would have been superlative had the OPT been larger and CFB% been
15% instead of only 10%. Triode input plus triode driver tubes such as a
pair of 6CG7 would have been far better than the EF86 and the paraphase
splitter arrangement.

Well, yes, but the bottom line is that Quad never went out for more
power, as the ESLs could not handle much more, and the Quad is more
stable than the Willy.

Any Williamson can be easily stabilised by use of gain/phase tailoring
between the phase splitter and balanced amp driver.


The Willy uses driver tubes after the splitter
and that only makes sense in Class AB2 or Class B2 service, and it
uses cathode bias like the Quad, which once reliable silicon diodes
came out was bad practice.

The driver balanced amp in a W amp are most suited to class A1 or AB1
use and they perform hopelessly badly just like the worse EF86 Quad
drivers if having to drive in to any grid current.
The only successful way to drive class AB2 or B2 (without using an IST)
is where you have direct coupled cathode follower buffers between the
voltage amp driver stage and OP tube grids. McIntosh have this. McI go
to a lotta trouble to squeeze 50W from apair of 6L6GC. Its largely
classAB1 mostly with some AB2 capability, so THD/IMD without all the NFB
they have is appalling, but with a lotta FB it measures well.
OK, but for 50W a quad of 6L6 and a simpler circuit with far less FB
achieves better results. A couple extra tubes are cheaper than the McI
type of OPT. Ditto the EAR509.

Willys also need to have individual cathode biasing like Leak so you
don't have the problems of bean counter inspired biasing arrangements in
Quad or the original W with a 250 ohm pot in the OP tube output circuit.


The flaw is that they COULD have used
triode output or a smaller beam power tube for the same basic power,
although the EL84 is not a particularly attractive hi-fi bottle to
me.

If Quad-II has tried to use a pair of real triodes for 20 Watts of class
A into 8ka-a, with lesser loads all giving class AB1 loading,
then they'd have had to use a pair of 300B pushed very hard or a quad of
KT66. KT88 were not available.
You see, each KT66 in CFB has Pda = 25 watts at idle for a total of 50W
and if max class A1 efficiency = 40%, then you have 20W of class A, and
not a drop more. There is precious little extra PO in class AB1 if loads
drop below the load for maximum class A1.
Now if you had KT88 in triode and biased for 25W Pda each so the tubes
are nice and relaxed, the max efficiency is only 33% and only if RL is
maybe 12ka-a and Ea = 500V, and you'd get 17 watts of class A1 triode.
With Ea kept low in Quad-II to give relibability with PS caps you just
can't get triode class A efficiency above 25%, and Po is only around 12
watts.

But the 12 watts from KT88, KT66, EL34 is always better than what you'd
get from EL84 in UL.
Baird used a sixpak of EL84 to get 60W class AB1, and in class A you
could get 27W with 6 tubes and the sound is then pretty good and quite
equal to anything else making 28W in UL class A1.

Quad took the medium road with KT66, a very well known and easily
available tube that had been around for 20 years+.
One can use 6L6 if you can't afford KT66.


Then again we could say the E type Jaguar was no good because it had
a lousy transmission..... It was and is a great car anyway, you just
put a Toyota or Richmond gear transmission in there and enjoy it.

I think cars are a necessary evil upon the planet.....

The Willy also ran a 10K load if you will remember.Dropping it very
much made it into not quite a Willy. A pair of 6L6GC/EL34/7027/KT66
should give 40 watts at reasonable dissipations and plate voltages and
20 is obtainable from EL84s or even 6V6s if one uses good
ventilation.

The W amp does work a bit into triode class AB1 when the load falls
below 10k in the original circuit.
But without fixed bias or separate Rk with decent bypass caps the W is
hopeless when the anode load drops in triode, or in UL mode if that's
how it is used.

Power ability isn't the only issue for hi-fi. 40W from a pair of KT66 in
a UL Williamson is available, but you'd never need that much powerwith
ESL57 which is mostly a high impedance speaker.

Of course Quad do make a Quad40 with KT88 and the 40 watt power max then
is like a bonus for anyone who doubts ESL57 don't quite give their best
with Quad-II. Having 40 watt capability with KT88 means that the first
few watts are going to be cleaner and with less THD/IMD and the amp is
probably less prone to the bias drift one sees in Quad-II amsp and the
sound wrecking Ia imbalances in each 1/2 of the OPT primary.

But I have never seen the Quad40 schematic. I'm told its the same as the
Quad-II, with all the same weaknesses which is a shame if that's the
case.

And Lord knows what Paravicini has put into the Quad80.



Hammond is a good company but their output transformers are really
not the highest spec and are best used in guitar amps or for jukebox
or Hammond organ resto's.

It depends how you use the Hammonds.

I've build a few amps with them and used them to replace the woeful
Chinese efforts in Jolida amps and the customers were very happy.

You have to realise that although its nice to know you have really wide
bandwidth OPT even at full clipping power, the fact is that the
artifacts from limited HF and low frequency saturation do not affect the
sound hugely at the 1 watt average level which is actually more than
most people ever use if their speakers average say 90dB/W/M.
The HF limiting and LF saturation is a voltage related phenomona so that
at low output levels of 1/10 full power at 1/3 full voltage the
saturation is reached at 10Hz instead of 30Hz for full po, and
similarly, HF saturation extends to 60khz without distortion at the
lower level.


The best value for a DIYer right now is the
load of Mc MA230 (not unity coupled, a conventional EI wind by
Endicott Coil) outputs floating around for well under $100 each,
followed by the limited but well executed Peerless clones being done
by a company in Michigan. (I wouldn't have anything Magnequeef stuck
up my ass).

Magnaqueer is a dirty word to some around here, but others you mention
still produce music.



The Marantz 8B was factory rated at 35 wpc with a pair of EL34s, and
used a transformer Mikey tried to tell us was a ripoff of a Peerless
but he is full of shit. Magnetic Windings (Easton, PA.) wound them for
the VAC repros and will wind them for you if you order 50 too. I
suspect that along with the Radford , the Marantz 8B was probably the
best commercially built hi fi tube amp of all time from the mainstream
tube era.

35W max from 2 x EL34 merely indicates an AB1 PO count like from the
Dynaco ST70. If there is a 4 and 8 ohm outlet, and you have 8 ohm
speakers then you plug the 8 ohms into the 4 ohm outlet, the amount of
pure class A rises, distortion is halved, Rout is halved, and bandwidth
slightly widened but at the expense of reducing max PO to around 25
watts.

With average speakers i don't know anyone who needs more than 25W for
99% of their listening. Some will imagine they are being short changed
and that their amp is labouring or clipping with a high Z speaker
connected to a low Z outlet.

I cannot much help those who imagine things, except to say they ought to
measure the real Z of their speakers, and take some voltage measurements
which give a peak and hold facility, and they'd be surprised at how
little PO they actually need to have.


Patrick Turner.
.

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